Sensor devices of this type are mainly used as light sensors for controlling the vehicle lighting. The use of traditional lenses to influence the beam path, such as, e.g., the lenses, inclined towards the windshield, of the rain sensor shown in EP 1 068 112 B1, requires a comparatively large amount of space.
The use of holographic structures allows to realize smaller designs, as known from, e.g., WO 03/026937 A1. These sensors are based on the principle of light diffraction with the aid of diffractive elements and therefore have the principle-induced drawback of a substantially lower useful luminous efficiency and a higher sensitivity to stray light.
In connection with an optical sensor device, DE 196 08 648 C1 proposes configuring the light entry and exit surfaces of the optical waveguide unit in the form of Fresnel lenses. But since the surfaces of the optical waveguide in which the lenses are configured are perpendicular to the surface of the pane, this device requires a very large amount of space.
Further basic disadvantages of known optical ambient light sensor devices are found in the high production expense and in a reception range which is too small. The attempt in connection with sensor devices having Fresnel lenses to expand the reception range in that the light receiver is placed further away from or closer to the focal point of the Fresnel lens is unsuccessful because this is accompanied by a splitting of the receiving characteristic into one or several further ray beams far out of the reception range provided. This also applies to the attempt to increase the receiver area.
It is an object of the invention to increase the reception range of the sensor unit while avoiding the aforementioned drawbacks.